podzol

podzol

(pŏd`sŏl) or

podzolic soil,

member of a group of soils that are gray in color, have an ashy appearance, and extend immediately south of the tundra regions of the Northern Hemisphere. Although characteristically capped with an abundant surface accumulation of organic matter, these soils are often severely leached and highly acid. They are thus generally low in agricultural value, forests being their most common and practical coverage. South of the podzolic soils, prairie soils are sometimes found. These dark semipodzolic soils have unusual fertility owing primarily to a vegetative cover of grass rather than forest. They are generally leached free of carbonate but retain mineral fertility.

Podzol

any one of a group of acid soils. The process by which podzols are formed (podzolization) involves the transformation of parent soil under the influence of acid hydrolysis and the removal of silt and bivalent and trivalent metals from the top eluvial horizons of the soil profile into the illuvial horizons, where silica is accumulated. This removal from one horizon to another results from the movement of organic mineral compounds and from the leaching of silt particles out of the upper layers into the lower ones without preliminary destruction of aluminosilicates. Podzolization occurs in parent soil regardless of the particle size if the surface soil horizons are intermittently waterlogged and have an acid pH and a leaching regime.

Podzols were first described by V. V. Dokuchaev in Smolensk Province in 1879. They are characterized by an acid pH, differentiated soil profile, scarcity of silt and trivalent metals in the upper horizons, relative abundance of silica in these horizons, and a thin eluvial-humus horizon or even the absence of such a horizon. Fulvic acids are predominant over humic acids in the humus. The following horizons are distinguished in the profile of podzols: Ao (forest litter), 1–10 cm thick; A1 (eluvial-humus), 1–20 cm thick, characterized by gray color, powdery texture, friability, and a 1–6 percent humus content; A2 (podzolic), 2–20 cm thick (sometimes more), characterized by light gray (almost white) color, lamellar texture, friability, and the presence of loamy and clayey podzols containing hardpan; B (illuvial), 10–50 cm thick, characterized by soil that is compact and coarser in particle size than the soils of the upper horizons, grayish brown color, and a coarse polyhedral, less commonly prismatic, texture; and C (parent soil).

The following subtypes of podzols are found in the forest zone of northern Europe, Siberia, the Far East, central and southern Canada, and the northeastern United States: gley-podzolic, podzolic, sod-podzolic, and sod-pale-yellow-podzolic. Interzonal interspersions of these subtypes may be found as a result of local peculiarities of soil formation. Subtropical and tropical podzols have been described in the Amazon River basin, in the tropics of Asia and Africa, and in Colchis in the USSR. The subtypes are further divided into genera and species according to the nature of the parent soil and some characteristics of recent and relict soil formation.

In the forest zones most of the land used for agriculture and forestry is podzolic. Land with loamy and clayey podzols is comparatively well supplied with moisture, and winter grains may become waterlogged in wet years. Moisture is least in soils of fine particle size and during periods of drought. Podzols should be limed and treated with organic and mineral fertilizers. They can be effectively used in forestry and for growing crops.

Podzol

[′päd‚zȯl]

(geology)

A soil group characterized by mats of organic matter in the surface layer and thin horizons of organic minerals overlying gray, leached horizons and dark-brown illuvial horizons; found in coal forests to temperate coniferous or mixed forests.

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